Keeping the fungi away: did warm bodies put mammals on top in evolutionary history?

Did a warm body put mammals at the head of the evolutionary rat race? Aviv Bergman and Arturo Casadevall present evidence in an Observation piece in mBio this week that the warm mammalian body is no accident and our relatively high body temperature could represent the perfect evolutionary compromise between metabolic costs and the increased fitness that comes with resistance to fungal diseases.
Using a computer model, Bergman and Casadevall pitted the cost of maintaining excess metabolic rates that keep mammalian body temperature high against the benefits of evading those nasty fungal infections. Their calculations show that the ideal body temperature to minimize costs and maximize fitness falls at 36.7°C – very close to the average mammalian body temperature. To Bergman and Casadevall, this supports the idea that overcoming susceptibility to fungal disease was a key to mammals’ success during the Tertiary geologic period, a time when mammals supplanted reptiles as the dominant land-based vertebrates.